The present invention concerns a device directed to a continuous control of a piezoelectric actuator for fuel injection systems.
To control fuel injection valves for internal combustion engines, previously proposed systems, as described in German Published Patent Application No. 195 31 652, use piezoelectric actuators whose piezo stack, that changes in length in response to an electrical control voltage, serves to actuate the valve element. With piezoelectric actuators, a pronounced hysteresis effect arise between the electrical voltage applied to the piezo stack that receives the electrical charge and the generated elongation of the piezo stack during the operating cycle. Due to this dielectric hysteresis, the high precision in the set movements of the fuel injection valves from piezoelectric actuators cannot be maintained.
Furthermore, it is difficult to continuous control the actuators due to alternating conditions of use and operation of i.c. engines such as load and temperature, and to the ageing of the piezo stack.